The beetle looks like Pterostichus niger and the non-swollen front tarsae (segments of the 'foot') makes it a female - so her abdomen is probably swollen for good reason. This is the look that a lot of beetles have when they are 'gravid' and full of eggs - its the right season too, so that would be my somewhat informed opinion. Other hypotheses would include parasites, an internal nematomorph worm (Nematomorpha) perhaps .... but I still favour that she is simply 'pregnant'.